The present invention relates to a process for the pre-isomerization of hops, in particular for preparing a beer or like beverage.
It is known that beer is usually prepared from malt, i.e., germinated barley, from which a sugared wort is prepared in a treatment termed brewing, this wort being then subjected, after cooling, to a fermentation in the presence of yeast to obtain an alcoholized beverage. The malt is first of all crushed in a mill and the flour obtained is mixed with water in a hydrator for the pasting operation. The solution obtained is then conveyed to a material vat in which the saccharification of the starch occurs.
The sugared wort thus obtained is then subjected to the successive operations of filtration, cooking and hopping.
The hops are therefore a traditional additive in brewery which, when added to the sugared wort, imparts to the beer in particular its gustative and thirst-quenching qualities by its bittering power.
Now, in order to be effective, the hops must undergo before use an isomerization of its active principles. These conditions of isomerization of its active principles and exhaustion of the hops in a conventional brewing hall adapted to produce brewer's wort are particularly bad.
Indeed, the low pH of the wort, the absorbent power of the cloudy part, among other factors, limit the transformation of this raw material and gives a particularly poor hopping yield, on the order of 20 to 30%, this yield being the higher as the hopping is low. Furthermore, the chemistry of the hops is excessively complex and among the parts of the hops of use in brewery there are principally the essential oils, resins, waxes, lipids and tannins.
The essential oils are formed by a fraction of lupulin which is distillable with steam, non-miscible with water and is a complex mixture of hydrocarbons and oxygenated compounds.
The resins and the essential oils perform in the beer an aromatizing function and two acids are found in the resins which impart to the hops its bittering power and antiseptic power, namely humulon and lupulon.
In the course of the treatment of the hops, it is necessary to take into account the fact that the essential oils are volatile, i.e., the hops must not be allowed to cook for an excessively long period.
As concerns the bitter resins, they on the contrary require a rather long boiling, on the order of one hour, so as to be solubilized in a stable manner after polymerization.
Further, the boiling also increases the colouring of the beer; this is due partly to the conversion of the sugars into caramel and partly to the oxidation of the tannin of the hops.
Moreover, the hops is an expensive raw material and it is advisable to use it under optimum exhausting conditions.
This is why at the present time a certain number of methods have been developed for pre-transforming the hops before it is used in brewing, for the purpose of improving the yield. These methods employ chemical artifices which are not authorized by every beer-producing country.
Up to the present time, the techniques of isomerization employed the conversion of an alkali solution. But the alkali and the temperature bring about a change in the composition of the hops. This isomerization has a yield of at the most 80% since a proportion of the iso-alpha acids is hydrolized into non-bitter humulinic acids. One of the problems with isomerized hops is their stability, since the isomerization is sensitive to variations in temperature, pH and the composition of the medium.
The addition of isomerized extracts of hops to the filtered beer is generally not practiced in a commercial way, since, when added in this way, they have a tendency to render the beer more cloudy. However, it is obvious that the later this hops are added in the beer-preparing process, the higher the yield.
Generally, the isomerized hops are diluted in water and, as a certain time is required to allow them to become diluted in the beer, this product is added at the beginning of the keeping period and not at the end. In order to promote this dilution, the isomerized hops are added to the beer in a turbulent state, i.e., in a pipe or pump. The major part of the losses of hops occurs in fermentation and it is therefore preferable to add the isomerized extracts with their alkaline salt after the fermentation, namely just before or just after the filtration.
But the main defect of the beer employing this kind of hops is the exaggerated frothing.